Observation Of Supercurrent Research Articles

Creation of equal-spin triplet superconductivity at the Al/EuS interface

In conventional superconductors, electrons of opposite spins are bound into Cooper pairs. However, when the superconductor is in contact with a non-uniformly ordered ferromagnet, an exotic type of superconductivity can appear at the interface, with electrons bound into three possible spin-triplet states. Triplet pairs with equal spin play a vital role in low-dissipation spintronics. Despite the observation of supercurrents through ferromagnets, spectroscopic evidence for the existence of equal-spin triplet pairs is still missing. Here we show a theoretical model that reveals a characteristic gap structure in the quasiparticle density of states which provides a unique signature for the presence of equal-spin triplet pairs. By scanning tunnelling spectroscopy we measure the local density of states to reveal the spin configuration of triplet pairs. We demonstrate that the Al/EuS interface causes strong and tunable spin-mixing by virtue of its spin-dependent transmission.

Supercurrent in the quantum Hall regime.

A promising route for creating topological states and excitations is to combine superconductivity and the quantum Hall (QH) effect. Despite this potential, signatures of superconductivity in the QH regime remain scarce, and a superconducting current through a QH weak link has been challenging to observe. We demonstrate the existence of a distinct supercurrent mechanism in encapsulated graphene samples contacted by superconducting electrodes, in magnetic fields as high as 2 tesla. The observation of a supercurrent in the QH regime marks an important step in the quest for exotic topological excitations, such as Majorana fermions and parafermions, which may find applications in fault-tolerant quantum computing.

Observation of supercurrent in PbIn-graphene-PbIn Josephson junction

Superconductor-graphene-superconductor (SGS) junction provides a unique platform to study relativistic electrodynamics of Dirac fermions in graphene combined with proximity-induced superconductivity. We report the observation of the Josephson effect in proximity-coupled superconducting junctions of graphene in contact with ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{In}}_{x}$ ($x=0.07$) electrodes for temperatures as high as $T$ $=$ 4.8 K, with a large value of ${I}_{c}{R}_{N}$ ($~$255 $\ensuremath{\mu}$ V). This demonstrates that ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{In}}_{x}$ SGS junction would facilitate the development of the superconducting quantum information devices and superconductor-enhanced phase-coherent transport of graphene.

Observation of supercurrent in single InAs self-assembled quantum dots coupled to superconducting leads

We report a first direct observation of proximity supercurrent in a single InAs self-assembled quantum dot coupled to superconducting electrodes. We utilize large SAQDs with strong dot-lead coupling allowing sufficient overlap of quantized state that charge fluctuation in the dot may exceed one electron. Although the charging energy is larger than the superconductivity gap, Δ, the voltage characteristic measured in the current-driven four-terminal geometry signifies a supercurrent flow though the dot. The observed critical current is of the order of 10 pA, and much smaller than expected from theory. This current also shows the parity effect with the number of electrons in the dot, suggesting that the singlet correlation impedes the Cooper pair tunneling.